Process for the production of a dense stitched fleece

ABSTRACT

A continuous process for producing a dense and compact stitched fleece is disclosed wherein a stitched fleece comprised of at least two fibers having defined melting points, one of the fibers having a melting point lower than the other fibers and being used as binding fibers, is heated in the range of the temperature of the binding fibers to soften said binding fibers; the stitched fleece is compressed while said binding fibers are in the softened state; and the stitched fleece is cooled to solidify the fleece while the fleece is in the compressed state. In addition, the product of this process and the apparatus for effecting the process are disclosed.

United States Patent Fleissner 5] Apr. 8, 1975 [5 1 PROCESS FOR THEPRODUCTION OF A 3.515.609 6/l970 Rudlofi 264/113 3.620.892 11/1971Wincklhofer et al. 264/122 DENSE STITCHED FLEECE PrimaryE.\'ami11erRobert F. White Assistant Examiner-.1. R. Hall Attorney.Agent. or F inn-Craig & Antonelli [57] ABSTRACT A continuous process forproducing a dense and compact stitched fleece is disclosed wherein astitched fleece comprised of at least two fibers having defined meltingpoints. one of the fibers having a melting point lower than the otherfibers and being used as binding fibers. is heated in the range of thetemperature of the binding fibers to soften said binding fibers; thestitched fleece is compressed while said binding fibers are in thesoftened state; and the stitched fleece is cooled to solidify the fleecewhile the fleece is in the compressed state. In addition. the product ofthis process and the apparatus for effecting the process are disclosed.

18 Claims, 2 Drawing Figures [75] Inventor: Heinz Fleissner, Egelsbach,Germany [73] Assignee: Vepa AG, Basel. Schweiz.

Switzerland [22] Filed: Feb. 17, I970 [21] Appl. No.: 14,808

[30] Foreign Application Priority Data Feb. 25. 1969 Germany 1909345Feb. 17. 1969 Germany 1907860 [52] US. Cl 264/122; 264/92 [51] Int. ClD04h 1/54 [58] Field of Search 264/122, 113, 92

[56] References Cited UNITED STATES PATENTS 2,852,485 9/1958 Stoff etal. 264/122 3.431.334 3/1969 Williams et al. 264/122 PROCESS FOR THEPRODUCTION OF A DENSE STlTCl-IED FLEECE BACKGROUND OF THE INVENTION Thepresent invention relates to a process for producing a dense stitchedfleece suitable base material (substrate) for synthetic leather, and inparticular to a process for producing a densely stitched fleececomprising at least two types of fibers, one of which is employed as thebinding fiber. This fleece, which is suitable as a base material forsynthetic leather, can be strengthened by means of a thermal treatment.

It is conventional to utilize fleeces as a base material for syntheticleather. These fleeces generally contain a large proportion ofhigh-shrinkage fibers, for example about 30-50%, or more. In casehigh-shrinkage fibers of polyesters or polyamides are employed. theshrinking step is most advantageous conducted in a water bath heated toa temperature of about 90-95C. However, in this connection, considerabledifficulties are encountered in obtaining a uniform shrinkage over aspecific width of the material. A uniform shrinkage is necessary sincethis produces the desired closeness density in the material. Only whenthe density is uniform is it possible to obtain uniform properties insynthetic leather. When using polypropylene as the shrinkage fiber, theshrinking step is carried out in heated air. By means of the shrinkingprocess, a very close, dense and compact fleece is obtained exhibiting acorrespondingly good flexural elasticity. Becuase of the difficultyencountered in obtaining a uniform shrinkage, it is also known to employknitted and woven fabrics as the base. These fabrics are expensive intheir manufacture, and the final products do not possess propertiesequal to a synthetic leather utilizing a shrunk fleece as a basematerial. In order to avoid the difficult shrinking process, it has alsobeen suggested to use a stitched fleece as a base (carrier or substrate)material, said fleece having a certain proportion of binding fibers.These fleeces are very voluminous and do not exhibit the closeness of ashrunk fleece and thus do not exhibit the good properties of a shrunkfleece.

SUMMARY OF THE INVENTION An object of the present invention is to avoidthe prior art disadvantages in providing a process for pro ducing astitched fleece suitable as a base material for synthetic leather.

Another object of the present invention is to provide an improvedprocess for producing a base material for synthetic leather wherein agood bonding of the individual fibers and a uniform compactness of thefibers is achieved.

A further object of the present invention is to avoid the difficultiesencountered in the treatment of shrunk fleece but, at the same time,imparting to the base material the similar advantageous properties of ashrunk fleece.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter; it would be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications with the spirit and scope of theinvention will become apparent to those skilled in the art from thisdetailed description.

Pursuant to the present invention, it has been found that theabove-mentioned disadvantages may be eliminated and a much improvedprocess for producing a base material for synthetic leather may beobtained by heating the stitched fleece to the melting or softeningtemperature of the binding fiber, compressing the fleece, and thencooling the fleece during the compression step. The compression(pressing) step effects, on the one hand, a very good bonding of theindividual fibers to one another by welding, and, on the other hand, aconsiderable compacting of the fleece. By cooling the fleece during thepressing step, the fleece is simultaneously solidified in the compressedcondition, so that as a result thereby a very close fleece is producedwhich, additionally, is also extremely uniform, particularly in itscloseness (compactness).

it is advantageous to conduct the heating process utilizing air, steam,or a steam-air mixture as the treat ment medium, wherein this treatmentmedium is drawn through the fleece. ln order to compress the fleece, atleast one pair of cooled rolls can be employed, and for coolingpurposes, air can be utilized.

It is furthermore advantageous to hold the fleece compressed between aperforated drum and a perforated belt, at least during the cooling step,and to guide it therebetween, with a gaseous or liquid cooling medium.e.g., air, steam, or water, being conducted through the fleece andthrough the drum and belt during the cooling process. The feature ofstarting the compression of the fleece while it is in the plasticcondition of the melt fiber afford the advantage that a moresatisfactory welding is achieved due to the relative movement of theindividual fibers with respect to one another. A particularly goodfleece for a base material for synthetic leather is obtained accordingto the present process by providing that the fleece contains up to about50% binding fibers, preferably about l0-l 5% binding fibers, and isstrengthened by a thermal treatment and a pressure treatment asdescribed above. By increasing the proportion of binding fibers withinthe desired proportions noted above, the closeness of the fleece can beenhanced.

A fleece consists of a specific fiber having a specific melting point.If another fiber having a different chemical composition and a lowermelting point is added to this fiber, it serves as a binding fiber whenthe temperature of the fleece is increased in the range of the melt ingpoint of said another fiber. Thus, the fleece as defined by the presentinvention comprises at least two of any material of synthetic fibershaving a defined melting point, at least one of said fibers having amelting point lower than that of the remaining fibers.

The fibers which can be utilized by the present inven tion include anyof the natural or synthetic fibers. The natural fibers can includecotton, wool, silk, cellulose, etc., and the synthetic fibers maycomprise synthetic polymers such as polyolefins, e.g., polyethylene,polypropoylene, etc., polyamides, e.g., Nylon 6 obtained by condensationof caprolactam, Nylon 66 obtained by the condensation ofhexamethylenediamine with adipic acid, etc., polyesters, e.g.,polyethylene terephthalate, etc., phenolic resins, e.g., phenolformaldehyde resins, urea formaldehyde resins, etc., polyvinylmaterials, e.g., polyvinyl chloride, polyvinyl acetate etc., andacrylate resins, such as polymethylmethacrylate. Copolymers of thesematerials with one another or with ethylenically unsaturated monomers,and similar type polymers are also encompassed by the present invention.Typical fleece compositions include. for example. polyester fibersutilizing polypropylene or polyamidcs as the biniding fiber.

A good. uniform coaiescence and thus a fleece which possesses anextraordinary uniform strength is obtained by combining the two types offibers to a bi-component fiber. Such a fleece can also be advantageouslyproduced as a spun fleece from endless fibers. A fleece of this typeexhibits an especially high flexural elasticity and a wrinkle-recoveryangle of about l7()l 80C. Ex amples of bicomponent fibers include Nylon66 and Nylon 6. Orlon 2l. 2] and 27 a polyester with a polyamide. andHS] and Nylon.

For the manufacture of such fleeces. it is suggested to employ anapparatus containing at least one sieve drum subjected to a suctiondraft. for heating the binding fibers to the melting temperature. Also,a perforated belt which is associated with the sieve drum is provided inthe proximity ofthe outlet of the treatment chamber. said belt applyingan initial pressure against the sieve drum and the fleece disposedthereon. It is also advantageous to draw in by suction fresh air forcooling the fleece. at least in a portion of this zone.

It is also possible. in the case of certain fleeces. to provide afterthe sieve drum at least one pair of cooled compression rolls. in placeof such a perforated belt. A cooled pair ofcompression rolls can beadvantageously employed when treating thin fleeces wherein the coolingis extensively effected by contact with the compression rolls. In thecase of thick fleeces, an apparatus with the above-described perforatedbelt is more desirable.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become morefully understood from the detailed description given hereinbelow and theaccompanying drawings which are given by way of illustration only andthus are not limitative of the present invention and wherein FIG. 1shows a longitudinal section through the apparatus for carrying out theprocess of this invention;

FIG. 2 shows a cross-section through the apparatus of FIG. I along lineAA of FIG. I.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings. the apparatus for effecting the process of the presentinvention comprises a heat-insulated housing 1, containing a sieve drum2, sujbected to a suction draft. Above and beneath the sieve drum 2,heating elements 3 are provided for heating the circulated treatmentmedium. for example air and/or steam. At the front face thereof, thesieve drum is provided with a fan 4, which draws the treatment mediumout of the sieve drum and blows medium back to the outer surface of saidsieve drum, via additional heating elements 5. In the sieve drum 2, acover plate 6 is arranged at that side of the sieve drum, which is freefrom the material being treated. The cover plate 6 prevents thetreatment medium from entering the sieve drum 2 at this side. The fleece7 to be strengthened is fed to the sieve drum 2 on a conveyor belt 8, inthe apparatus shown in the drawing, and is suddenly heated. in ashock-like manner i.e.. the fleece is rapidly heated. to the treatmenttemperature. by drawing the treatment medium into the drum through thefleece disposed on the sieve drum. A perforated belt 9 is associatedwith a portion of the periphery of the sieve drum. said belt. which isunder tension or pressure. functioning to compress the fleece. Byutilizing this compressing step, a more satisfactory welding together ofthe binding fibers with the other fibers is accomplished. AT the sametime, the fleece is prevented from lateral shrinking by means of thebilateral guidance provided by the drum and the perforated belt. This isparticularly important when polypropylene is employed as the binding orshrinking fiber. In the prox mity of the outlet of the apparatus. freshair is drawn into the treatment chamber through an opening 10. Thisfresh air cools the fleece between the perforated belt 9 and the sievedrum 2, and thus the fleece structure is solidified in the compressedstate. In place of cooling by means of fresh air. it is also possible toeffect the cooling by a pair of cooled compression rolls ll arranged atthe outlet of the apparatus. However. this pair of compression rolls 11can also be additionally provided. The fan drive 12 and the drum drive13 are attached at the outside of the housing I.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention. and all suchmodifica tions as would be apparent to one skilled in the art areintended to be included.

What is claimed is:

l. A continuous process for producing a uniformly compacted stitchedfleece, which comprises:

a. providing a stitched fleece consisting essentially of at least twotypes of fibers having defined melting points, at least one type ofsaidfibers having a melting point lower than the others and being employedas binding fibers;

b. heating the stitched fleece to soften said binding fibers in thefleece;

c, compressing the heated stitched fleece while said binding fibers arein said softened state; and

d. cooling the heated stitched fleece while said fleece is in thecompressed state whereby the fleece is retained in said compressed stateupon solidification of said binding fibers.

2. The process of claim I, wherein the stitched fleece is cooled duringat least a portion of the compressing step.

3. The process of claim 1, wherein the stitched fleece is cooledsubsequent to the compressing step.

4. The process of claim 2, wherein the stitched fleece is further cooledsubsequent to the compressing step.

5. The process of claim I wherein the heating step (B) is conducted byutilizing a heating medium selected from the group consisting of air,steam and a steam-air mixture, said heating medium being drawn throughthe stitched fleece.

6. The process of claim 2, wherein the stitched fleece is cooled bydrawing air therethrough.

7. The process of claim 1, wherein the binding fiber is present in anamount of at least about 10%.

8. The process of claim 1, wherein the binding fiber is present in anamount of about 10 t0 l5% by weight.

9. The process of claim 1, wherein the fleece comprises polyester fiberscontaining polypropylene as the binding fiber.

10. The process of claim 1, wherein the fleece comprises polyesterfibers containing polyamides as the binding fiber.

11. The process of claim 1, wherein the fleece contains a bi-componentfiber selected from the group consisting of Nylon 66 -Nylon 6. Orlon2l-23-27 and a polyester-polyamide mixture.

12. The process of claim 1, wherein the stitched fleece is heated to atemperature near the melting temperature of the binding fibers to softensaid binding fibers.

13. A continuous process for producing a uniformly compacted stitchedfleece which comprises:

a. providing stitched fleece consisting essentially of at least twotypes of fibers having defined melting points, at least one type of saidfibers having a melting point lower than the others and being employedas binding fibers;

b. heating the stitched fleece to soften the binding fibers by conveyingsaid fleece on the surface of at least one sieve drum means subjected toa suction draft and by drawing a heated gaseous treatment medium throughsaid fleece;

c. simultaneously compressing the fleece between at least a portion ofthe surface of the sieve drum means and a perforated belt operativclyassociated with said sieve drum means; and

d. cooling the heated stitched fleece to solidify the binding fibers insaid fleece while said fleece is still in the compressed state.

14. The process of claim 13, wherein said gaseous treatment medium isselected from the group consisting of air. steam and a steam-airmixture.

15. The process of claim 13, wherein the fleece is cooled by drawing airthrough said fleece while still disposed between the sieve drum meansand the perforated belt 16. The process of claim 13, wherein the fleeceis cooled after being removed from the sieve drum means by conveying thefleece through a pair of cooling rolls.

17. The process of claim l5, wherein the fleece is further cooled afterbeing removed from the sieve drum means by conveying it through a pairof cooling rolls.

18. The process of claim 13, wherein the compressed stitched fleeceexhibits a high flexural elasticity and a wrinkle-recovery angle ofabout ll80.

2. The process of claim 1, wherein the stitched fleece is cooled duringat least a portion of the compressing step.
 3. The process of claim 1,wherein the stitched fleece is cooled subsequent to the compressingstep.
 4. The process of claim 2, wherein the stitched fleece is furthercooled subsequent to the compressing step.
 5. The process of claim 1wherein the heating step (B) is conducted by utilizing a heating mediumselected from the group consisting of air, steam and a steam-airmixture, said heating medium being drawn through the stitched fleece. 6.The process of claim 2, wherein the stitched fleece is cooled by drawingair therethrough.
 7. The process of claim 1, wherein the binding fiberis present in an amount of at least about 10%.
 8. The process of claim1, wherein the binding fiber is present in an amount of about 10 to 15%by weight.
 9. The process of claim 1, wherein the fleece comprisespolyester fibers containing polypropylene as the binding fiber.
 10. Theprocess of claim 1, wherein the fleece comprises polyester fiberscontaining polyamides as the binding fiber.
 11. The process of claim 1,wherein the fleece contains a bi-component fiber selected from the groupconsisting of Nylon 66 -Nylon 6, Orlon 21-23-27 and apolyester-polyamide mixture.
 12. The process of claim 1, wherein thestitched fleece is heated to a temperature near the melting temperatureof the binding fibers to soften said binding fibers.
 13. A continuousprocess for producing a uniformly compacted stitched fleece whichcomprises: a. providing stitched fleece consisting essentially of atleast two types of fibers having defined melting points, at least onetype of said fibers having a melting point lower than the others andbeing employed as binding fibers; b. heating the stitched fleece tosoften the binding fibers by conveying said fleece on the surface of atleast one sieve drum means subjected to a suction draft and by drawing aheated gaseous treatment medium through said fleece; c. simultaneouslycompressing the fleece between at least a portion of the surface of thesieve drum means and a perforated belt operatively associated with saidsieve drum means; and d. cooling the heated stitched fleece to solidifythe binding fibers in said fleece while said fleece is still in thecompressed state.
 14. The process of claim 13, wherein said gaseoustreatment medium is selected from the group consisting of air, steam anda steam-air mixture.
 15. The process of claim 13, wherein the fleece iscooled by drawing air through said fleece while still disposed betweenthe sieve drum means and the perforated belt.
 16. The process of claim13, wherein the fleece is cooled after being removed from the sieve drummeans by conveying the fleece through a pair of cooling rolls.
 17. Theprocess of claim 15, wherein the fleece is further cooled after beingremoved from the sieve drum means by conveying it through a pair ofcooling rolls.
 18. The process of claim 13, wherein the compressedstitched fleece exhibits a high flexural elasticity and awrinkle-recovery angle of about 170.degree.-180.degree..